With an increase in traffic on a network in recent years, demand for transmission technologies for optical networks is increasing. OTN (Optical Transport Network) is mentioned as one of such technologies. OTN is a technology whose standardization has been carried out in ITU-T (International Telecommunication Union Telecommunication Standardization Sector).
In OTN, a variety of types of client signals, such as SDH (Synchronous Digital Hierarchy), SONET (Synchronous Optical Network) and Ethernet (registered trademark), which are received from an external network, can be contained and transferred.
More specifically, an edge router in OTN transmits a received client signal, adding control information including an overhead (Overhead: OH) and error correction bytes or the like to the client signal. Transmitting a received client signal by inserting it into the payload of an OTN frame is also described as “contain (or map) a client signal into the payload of an OTN frame”.
In the following, description is given of a technology for containing a client signal in the payload of an OTN frame. Here, an OTN frame in this case is called an OPUk (Optical Channel Payload Unit-k). The “k” takes numerical values such as 0, 1, 2, 3 and 4, and each OPUk has a different frame structure.
When transmitting a client signal, containing it in the payload of an OPU frame, to an external network, it is necessary to reproduce the client signal from the OPU frame. Here, in order to prevent the occurrence of large variation between bits in the reproduction, it is preferable that a transfer rate at containment and that at reproduction are as equal as possible.
AMP (Asynchronous Mapping Procedure) is mentioned as one of technologies for containing a client signal. In AMP, in order to make a transfer rate of the payload in an OTN and that of a client signal almost the same with each other, insertion point of data called fixed stuff needs to be adjusted and normalized. Due to that, a problem has arisen in that AMP cannot be applied to many types of client signals. Here, the stuff is data inserted in the payload of an OPU frame so as to adjust the transfer rate.
On the other hand, GMP (Generic Mapping Procedure) is mentioned as a mapping method capable of flexibly handling a variety of types of client signals or a new client signal appearing in the future. GMP is a technology standardized as ITU-T G.709. GMP is described also in Japanese Patent Application Laid-Open No. 2010-212890 (hereinafter referred to as “patent document 1”).
In GMP, it is possible to contain client data at constant interval, determining a mapping position of client data or of stuff from a ratio between a transfer rate in the OTN and that of a client signal. Because of no necessity of effort to adjust an insertion point of fixed stuff, GMP can be said to be a more flexible method than AMP method.
In GMP, a mapping position of client data or of stuff is determined using the following operational expressions.
(1) when the following condition is satisfied, client data (D) is inserted in the block number j of an OPU frame.(j×Cm(t))mod Pm_server<Cm(t);
(2) when the following condition is satisfied, stuff (S) is inserted in the block number j of an OPU frame.(j×Cm(t))mod Pm_server>=Cm(t);
Here, definitions of the symbols are as follows.
j: payload block number,
Cm (t): the number of data blocks to be contained (the number of data blocks of a client signal),
Pm_server: the maximum value of payload block number,
mod: remainder operator.
FIG. 13 shows a configuration of a circuit which directly represents the above-described mathematical expressions. The circuit in FIG. 13 consists of a multiplication circuit 201, a division circuit 202 and a comparison/determination circuit 203. In the following, operation of the circuit in FIG. 13 will be described.
First, in the multiplication circuit 201, a multiplication j×Cm(t) is performed to obtain a multiplication result S211. The multiplication circuit 201 outputs the multiplication result S211 to the division circuit 202.
Next, in the division circuit 202, a division of the multiplication result by Pm_server is performed to obtain a remainder S212. The division circuit 202 outputs the remainder S212 to the comparison/determination circuit 203.
In the comparison/determination circuit 203, the remainder S212 is compared with Cm(t). When the remainder S212 is smaller than Cm(t), the comparison/determination circuit 203 outputs a signal S213 taking “High”. When the remainder S212 is equal to or larger than Cm(t), the comparison/determination circuit 203 outputs a signal S213 taking “Lo”.
The comparison/determination result obtained by the comparison/determination circuit 203 is outputted as a client data position signal which becomes control information for inserting client data when the signal is “High” or for inserting stuff when the signal is “Lo”.
As described above, when implementing GMP described in patent document 1, a multiplication circuit and a division circuit are necessary. In practice, a multiplication circuit is made up of a plurality of addition circuits, and a division circuit is of a plurality of subtraction circuits. Due to that, there has been a problem in that a number of addition circuits and subtraction circuits are required and accordingly the circuit scale of a communication device necessarily becomes large.